Method of winding toroidal coils



March 31. 1925. v

' 1,531,681 F. Al JTY METHOD OF WINDING TOROIDAL COILS Original Filed March s, 1924 2 Sheets-Sheet 1 m4 ATTORNEYS March 31. 1925.

F. AUTY METHOD OF WINDING TOROIDAL COILS 2 Sheets-Sheet 2 Original Filed March 5, 1924 JNVENTOR I fl'llfi% Alli BY QQZM, 'QQLM,

1 WM M ATTORNEYS Patented li/lar: 31, 1925.

PATENT OFFICE.

FRANK AUT'Y, OF NEW YORK, N. Y.

METHOD OF WINDING TOROIDAL COILS.

Application filed March 5, 1924, Serial No. 697,063. Renewed February 17, 1925.

To all whom it may concern:

Be it known that I, FRANK Am, a citizen of the United States, and resident of New York city, in the county of New York and State of New York, have invented certain new and useful Improvements in Methods of Winding Toroidal Coils, of which the following is a specification.

My present invention is primarily concerned with the method of making toroidal coils, a more specific application being to corclcss toroidal wire coils.

In their application for wireless receivkl ing purposes, the theoretical and practical advantages of coreless or air-core toroidal coils have been freely recognized by those skilled in the art, but difficulty of economical production of such coils, satisfactory in mechanical construction and in operation, has prevented their general ado tion.

It is accordingly among the ob ects of the invention to provide from wire of gage ordinarily used for variocouplers, variom eters or transformers,'a toroidal coil, satisfactory in its electrical characteristics, capable of sustaining itself in a firm and durable structure and ca able of resisting rough handling though evoid of a core.

Another object is to provide a method for making a toroidal coil, which method can be executed expeditiously with simple apparatus to provide a toroidal coil, self-sustaining though devoid of a core, and which method in its execution will not engender undue frictional stresses 01' strains on the convolutions of the torus, tending to fray the insulating covering of the wire.

The invention embodies broadly the principle' of winding the wire or equivalent member in convolutions along a straight axis, said convolutions being specially conformed or arranged preferably inherently to lap with respect to each other particularly at the inner periphery as the straight coil is curved to bring its ends together in forming the torus. In the preferred mode of exeoutin' the invention, the convolutions are ormed in cyclicall repeated groups arranged for a degree 0 lap which is a maximum at the inner periphery of the torus, and decreases progressively to full exposure of the entire run of convolutions without lap at the outer periphery of the torus. Preferably the convolutions are so arranged as to lap at the inner periphery of the torus in a number of layers equal to the ratio of the outer to the inner periphery of the torus.

Inasmuch as the convolutionsmay have a tendency to spread or separate before curving into the torus, the consecutive convolutions are preferabl secured against such separation by bin ing along at least one of the elements of the helix, preferably that which forms the outer erlphery of the finished coil. The ends of the binding when joined will serve to maintain the toroidal coil in assembled relation.

In the preferred method of producing the toroidal coils, a collapsible mandrel is used upon which the lapping groups of convolutions are formed. The entire effective length of the preferred form of mandrel is provided with peripheral notches of appropriate shape, said. notches of maximum depth and width along one element of the generally cylindrical mandrel, progressively decreasing to a minimum, preferably zero depth and width at the diametrically opposite element of the mandrel. The crosssection of the notch being shaped with one side substantially radial of the mandrel and the other side inclined, it follows that in winding the wire thereon, the successive convolutions thereof will contact to cover the inclined side of the notch, whereupon thenext convolution will dro into the base of the succeeding notch, until the effective length of coil has been formed. The mandrel being of collapsible type is readily removed from the coil. The coil thereupon is easily curved to draw its ends together, the convolutions of minimum diameter readily lapping into the contiguous convolutions of maximum diameter at the inner or concave periphery of the torus thus formed.

Other objects and features of the invention will be in part obvious and in part set forth hereinafter.

The coil as an article of manufacture is separately claimed in my divisional ap lication, Serial No. 737,099, filed Septem r 11, 1924; and the mandrel as an article of manufacture and also the method ofmaking preferably V- the same is separately claimed in my divisional application, Serial No. 728,072,

filed July 25, 1924.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. 1 is a transverse sectional view through a toroidal coil shown mounted on an appropriate supporting fixture,

Fig. 2 is a plan view of the toroidal coil,

Fig. 3 is an end view thereof,

Fig. 4 is a view in cross-section on a greatly enlarged scale illustrating the lapping of the convolutions,

Fig. 5 is a fragmentary view of one form of mandrel for making the coil,

Fig. 6 is a sectional view taken along the line 6-6 of Fig. 5,

Fig. 7 is a diagrammatic view illustrating the method of making the mandrel,

Fig. 7 is a fragmentary view of the tool used in cutting the mandrel.

Fig. 8 is a view in transverse cross-section taken alon the line 8-8 of Fig. 6,

Fig. 9 is a fragmentary view on an enlarged scale illustrating the method of winding the wire upon the mandrel of Fig. 6,

.Fig. 10 is a view similar to Fig. 9 of a modified form of the invention,

Fig. 11 is a view similar to Fig. 9 illustrating another manner of windin Fig. 12 is a diagrammatic view illustrating the mode of connecting the courses in the embodiment of Fig. 10, and

Fig. 13 is a view similar to Fig. 10 of a further modification.

Similar reference characters refer to similar parts in different views of the drawings.

Referring to the drawings, I have shown in Figs. 1, 2 and 3 in outline the general form of coreless toroidal coil with which my invention is primarily concerned, said coil being illustratively indicated withan outer periphery 10 substantially triple the inner periphery 11 thereof and held in as- .mounted on a bracket surface modified sembled relation by a peripheral length of tape 12 connected about the outer periphery thereof, the-terminals of the coil protruding as at 13.- The coil as shown, would be washers 14 and 15 near qgposite sides thereof, substantially'closing e inner peripher thereof and connected by a bolt -16 whic tends to curely grip the torus and which serves for mounting thecoil in manner that will readily be understood. 7 v

The construction of the toroidal coil will be more easily comprehended from the method of producing the same which will be first setforth. The mandrel by which the torus is rod ced, includes a winding from the cylindrical form as will appear best from Figs. 5 to 9. The

, one of the notches 21'.

including a pair of ress said washers inward to se-- mandrel construction will be most readily understood from the method by which it, in turn, is made. For this purpose, a tube of diameter equal to the inner diameter of the torus convolutions is mounted eccentrically, for instance, on centers 17 within a lathe (not shown). A tool 18 is employed having a cutting edge of buttress-thread type, that is, a V- haped cutting edge with one side 19 substantially longitudinally of the tool shank and the other side 20 oblique as best shown in 'Fig. 7. The tool being held by an appropriate rest (not shown) so that its point substantially engages the mandrel at the element thereof nearest the eccentric mount, the mandrel is rotated, whereby, as will be easily understood, a peeripheral groove or notch V-shaped in crosssection will be cut, of maximum depth as at 21 at the side nearest the eccentric mount, progressively decreasing to'a minimum or zero depth at theside 22 diametrically opposite thereto. The operation set forth is repeated at intervals corresponding to the cutting width of the cutting tool, so that the entire effective length of the mandrel will be notched, as best shown in Figs. 5 and 9. It will be seen that as the depth of cut decreases, peripherally about the mandrel from the maximum at one side thereof, the. width thereof decreases correspondingly.

A plane oblique edge 23 is therefore formed. at each peripheralnotch. The portion 24 to the right of edge 23 remains cylindrical. The portion 25 to the left of oblique edge 23 is V-shaped in cross-section of maximum depth and width at the element w-a corresponding to the side 21 and gradually decreasing both in depth and width progressively about the mandrel in both directions to zero at the diametrically opposite element b-b, corresponding to side 22.

The mandrel described being mounted concentricall in a lathe or equivalent driving means, he wire or other element 26 to be wound thereon is applied at the base of When the mandrel is now rotated, the wire will form substantially a helix. Consecutive convolutions thereof will be in lateral contact with each other along the straight element bb at one side 0 the mandrel while at the diametrically opposite sidea-az, the consecutive convolutions will climb up the incline 27 of the notch 21' until after the apex 28' of the notch is reached, the next convolution 26 will drop into the base of the succeeding notch for consecutive turns to build up along the corresponding notch incline. Thus, the conformations of the successive convolutions will vary to correspond with the mandrel, the convolutions 26 engaging the bases of the notches having a maximum eccentricity or degree of flattening extending substantially entirely within the original cylinder from which the mandrel was cut, while the convolutions corresponding to the apex or outer edge 28' of the notches are substantially circular without eccentricity, since, as'will be seen, they substantially follow along an uncut ,part of the mandrel surface.

- The mandrel being of appropriate collapsible type, best shown in Figs. 5, 6 and 8 which Wlll be described hereinafter, it is removed from within the wound coil after the adhesive tape 12 has been applied along the element b-b of the latter. Thereupon the generall helical coil of wire can be easily curve to bring its opposite ends into engagement with each other, an appropriate generally conical fixture (not shown) being preferably used as a guide or template for this purpose, whereupon the ends are attached together by a. short connecting piece 12 of adhesive tape with the wire terminals 13 projecting. Preferably a length 120 of tape similar to tape 12 is rovided at the inside of the outer perip ery of the torus, said latter tape being, of course,

applied on the mandrel before the wire is wound, and extending along the substantially flat side of the mandrel to adherently attach itself to the aligned contiguous portions of the inner convolutions as the latter are formed. I

The strip of tape or other binding means, whether applied internally or externally, either while the wire is being wound oh the mandrel or after the wire has been wound,

and before removing the same from the mandrel, serves to retain the helical coilin proper condition for handling. The binding means acts in a manner as a backbone, extending along the aligned contiguous portions of the loops and preventing endwise' expansion of the helical coil 'or radial expansion of any of the convolutions which might otherwise take place upon removal from the mandrel by reason of the springiness of the wire. a

It will be seen that the coil when removed from the mandrel and before it is'curved into torus form, will present a segmented appearance, the convolutions being in contact with each other along element b-b but arranged in groups at other elements thereof. By reason of this segmental or stepped conformation, as the coil is curved to orm the torus, the successive segmented groups will readily lap or telescope with respect to each other, the convolutions of smaller diameter entering into the neighboring convolutions of larger diameter, the extent of entry or telescoping being, of course, a maximum at the inner periphery 11 of the torus formed by element aaof the helical coil and progressively decreasing by reason of the peculiar formation of the coils to zero at the outer periphery 10 formed by element b-b, where the consecutive turns are in lateral engagement without lap.

If desired, the mandrel may be flattened as along line 29 at the side 22 where the notches are of minimum or zero depth. The wire when wound on the mandrel will have its convolutions correspondingl flattened, and the plane determined by sald flattened ortions will more readily curve into a cylinder 29 forming the outer periphery of the toroidal .coil, than if the turns were cylindrical at the part of the helix that is to be curved into the outer periphery of the toroidal coil. Moreover, tape 12 applied to such flattened part) also will develop no folds or wrinkles in curving into a cylindrical loop as the torus is formed.

In the specific toroidal coil illustratively shown, the inner periphery is one-third the outer periphery, so that only one-third as many turns can be ex osed thereat, in lateral contact with each other than at the outer periphery. Accordingly, the successive convo utions are all exposed in lateral contact with each other to form the outer periphery of t atoms, and only every third convolution Wlll be exposed at the inner nents, the diametrically opposite sides of the same turns 0 having the same ex onents. Between the inner and the outer peripheries of the torus, by reason of the intermediate width and depth of the notches of the forming mandrel, the degree of telescoping or lapping between the successive contactin groups of convolutions will vary in-accor ance with the diameter of the torus thereat, so that the unit is self-sustaining and will not open or be distorted even under substantial pressure, the convolutions .being in mutually trussing relationship.

It will, of course, be understood that the number of convolutions at each step or notch incline 27 should correspond approximately to the ratio of the outer tothe inner peri herv of the torus. By the use of a man rel with corresponding width of notch relative to the'diameter of the wire, a toroidal coil with any ratio of outer to inner diameter can be produced.

By my method, the convolutions are conformed to naturally or inherently enter into trussing relationship of its turns forms a rugged durable self-sustaining torus 'coil, when taped exteriorly only at its outer periphery, and even this is not necessary, when the internal binder strip is used.

Any other binding or attaching means may be employed which will permit curving the helix into a torus and yet anchor the lengths of wire of which the helix is formed at predetermined intervals, as, for instance, at every turn against separation longitudinally and peripherally of the helix.

To render the mandrel collapsible, any appropriate construction ma be provided. In a preferred embodiment, the stepped cutting mandrel tube is slit longitudinally in a number preferably four segments 30, said segments embracin 31, which may be 0 vulcanite and which has protruding metal center pieces 32. The segments are maintained assembled upon the core by end caps 33 preferably formed with integral spacing fins 34 to maintain the uniformity of the narrow gap 35 between the successive mandrel segments. It follows, therefore, that after the coil has been wound on the mandrel, the latter is collapsed by simply removing one of the end caps and drawing out the core whereupon the multiplicity of segments of the mandrel tube will collapse within the coil andcan be removed without in any way distorting the wound product.

It is distinctly to be understood that although the method set forth for winding the generally helical coil on my mandrel is preferably applied to'the production of my toroidal coil, and although the toroidal coil of my invention is preferably roduced by the method set forth, the metho may be applied to the formation of articles other than toroidal coils, and my coil is claimed per se regardless by what method it may be made.

While a preferred form of coil includes a series of convolutions which are contiguous at the outer circumference-of the coil and overlapping at the inner circumference, it is within the scope of the invention from its broader aspects, to provide a coil in which the convolutions are contiguous at the inner.

circumference and spaced apart at the outer circumference. The binding strip or other binder or binders in any of the embodiments of my invention, may extend about any one or more peripheries of the toroidal coil, but preferably a binder extends about the limiting periphery of maximum rather than that 'of minimum length, that is, about the outermost periphery of the torohl al coil.

In Fig 10 is shown a somewhat modified form generally similar to that described except that instead of forming the oblique side 27 of each notch straight in cross-section, the same is formed curved in cross-section as shown at 36. By this curvature in some a solid cylindrical core cases, the lapping or telescoping action in curving the helix into the torus may be somewhat facilitated.

In Fig. 11 is shownanothcr embodiment employing a mandrel 37 identical either with that shown in Fig. 9 or with that shown in Fig. 10 for winding a torus with a multiplicity of layers of turns, illustratively of small gauge wire. It will be understood, of course, that by appropriate mechanisms of known type, not material to the present invention, an inner layer 39 of convolutions would be laid on one incline 40 of the mandrel notch, the wire being thereupon fed back to the base of the same notch and a second layer 41 being formed, superposed over the first and, if desired, more layers, whereupon the succeeding convolutions would be dro ped off the point or apex 42 of the mandrel notch into the base 43 of the succeeding notch. After the co]- lapsible shaft has been removed, the completed coil would then be curved into a torus in the manner heretofore described.

By this arrangement, it will be seen that there is not the material difference in potential between successive layers which would result if one layer were wound complete and then connected in series with another layer wound thereover.

In Fig. 13 is shown a further embodiment which in certain special applications may be desirable, although in general, I prefer the embodiment shown in Fig. 5. The mandrel here instead of being formed with distinct peripheral notches is cut on a continuous thread, using, however, the identical buttress thread cutting tool 18 and mounting the mandrel in exactly the same manner as shown in Fig. 7 in the process of making the same. By this construction, the tool 18 being fed lengthwise of the mandrel, as in thread-cutting machines, a buttress thread 44 is formed of pitch equal to the maximum width of the individual notch out, which notch cut decreases both in width and depth peripherally about the mandrel to a minimum or zero at the diametrically opposite element 47 substantially as in the embodiment of Fig. 5.

When a coil is wound on the mandrel just described, it will be seen that it will be fed forward by the pitch of the thread 44, as best shown in Fig. 13. One such wire 48 having been thus wound along the mandrel, a second or independent wire (not shown) would be placed against the first and would thereby be wound in lateral contact therewith, whereupon a third, and depending on the dimensions of the torus to be produced, further wires would be wound, each in contact with the previously applied wire until the incline of the thread notch is substantially entirel covered. As indicated in the diagram of lg. 12, the left end 49, for inwinding control stance, of the first convolution would be connected by any ap ropriate coupling 50 1 to the left end 51 of the second convolution,

of the third convolution, etc., whereb the right end of-which would be Connected by a similar coupling 52 to the right end the entirelength of the wire .helix won (1 be series-connected. Thereafter the'helical coil would be curved to formthe toriis in the manner already described. I

While I have merely described in the foregoing a toroidal coil and the 'method of making the same, the principle of the invention could be readily. applied to simple .tuningcoils, to variocouplers, or variometers including two; semi-toroidal coils and to transformers, especially to radio frequency transformers. Inthe latter application, the primary coil of. lesser numberof convolutions could be wound in ordinary fashion about thesecondary after the latter had been made on the mandrel. In some of the applications noted, it'may be desirable to form the individual turns of the toroidal coil generally elliptical rather than generally circulara For this purpose, the mandrel would be formed as a generally elliptical cylinder,'

' with the notches heretofore described. 7 Alr so though the preferred application is, to corelessor air-core. coils, the invention. is not limited to this application, but may beeppliedto coils with coi'es performing eithera mechanical or a magnetic function or i? tion to wireless apparatus butcairbe applied The invention is not limited i.. its applicato other uses-and" many of the aspects there- .6: are more broadly applicable to winding and -40 P ng: p r fromclectrical application.

It willgthus be that th t. i sjl-Ehereixi I describedf'a''pparatus and a1method, i i-which. the several features of this invention are i. b di d, and which apparatus and method in its action attains the various objects of the invention and is well suited to meet the 7 requirements of practical use.

'As' many changes could be made 1n the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not' in a limiting sense.

Having thus described my invention, what I claim as new and dOSlIG to secure by Letters-Patent of the United States is:

1. The method of producing a toroidal coil, which consists in winding a wire into a generally. helical coil, with convolutions in side by side relation along one cylindrical element, and in groups or piles at the diametrically opposite cylindrical element, said groups lapping to form the inner periphery of the torus.

2. The method of forming a toroidal coil, which consists in winding a'continuous wire into a generally cylindrical helix having successive convolutions substantially in latby in curving the helical coil into a torus,

the groups of coils will lap .at the inner periphery and the flattened sides of the coils will determine a cylinderas the outer periphery.

4. The method of producing a toroidal coil, which consists in winding a wire on a mandrel in convolutions of radius substantially 'uniform at one side and along the opposite sides in cyclically repeated groups of graduated radii or stepped formation,

removing the mandrel from the coil and i curvingit into a toroidal form so that the stepped groups will telescope with respect to} ach' other at the inner periphery of the torus.

*5. The method of making a toroidal coil, which consists in winding a wire in a gen erally cylindrical spiral having the successive convolutions arranged in groups with radii varying in cyclic order along one element of the cylinder and then curving said spiral into a torus with the convolutions of smaller radius telescoping into contiguous convolutions of larger radius for regular arrangement of the convolutions at the central aperture of the torus.

6. In a method of producing a coil, the step which consists in winding a wire in a generally cylindrical spiral with successive convolutions lengthwise of the coil of uniform radius and substantially in lateral contact witheach other along one element of the cylinder and with successive convolutions along 'the diametrically o posite element in sets of cyclically varying radius,

' whereby the spiral coil canbe readily curved into a torus, the successive sets of coils lapping to form the inner diameter of the torus.

7. The method of forming toroidal coils, which consists in winding a wire into a generally cylindrical helix with convolutions flattened along one element of the cylinder in cyclic order, whereby in draw-- ing together the ends of the the torus,

automatically lap within a flanking convolution. 4

8. In the method of forming a step of winding a wire in cal' form with successive convolutions lengthwise of the coil substantially in lateral contact witheach other at one element thereof and with the convolutions at the diametrically opposite element thereof cyclically of reduced radius, whereby in curving the-helix with said former cylindrical element at the outside, the successive convolutions will contact at the outer periphery of the torus and the convolutions of reduced radius will lap with respect'to the flanking convolutions to expose at the inner torus periphery a lesser number of convolutions. 9. In the method of forming a torus coil, the step of winding a wire into a generally helical coil with successive convolutions lengthwise of the coil substantially in lateral contact with each other along one element of the cylinder and with the successiveconvolutions along the diametrically opposite element of cyclically varying radii with the number of convolutions of maximum radius at the latter cylinder element bearing a ratio to the total number of contorus, the a generally heli- 4 v'olutions corresponding to the ratio of the inner periphery of the torus to the outer periphery thereof, whereby in drawing together the ends of thecylindri'cal helix to form the torus the convolutions of smaller diameter will lap into the contiguous convolutions of larger diameter at the inside of the torus, so that in the finished torus the successive coils of maximum diameter will engage each other to form the inner periphcry of .the torus. 1

10. The method of forming a torus coil, which consists in windinga wire with successive convolutions thereof lengthwise of the coil substantially in contact with each other along-one element, said convolutions. of cyclically varyin radii for segmental conformation along tlie diametrically opposite element .of the cylinder, the depth of the segment conformation decreasing progressively about the convolutions to zero at the diametrically opposite element.

'11. The method of winding a torus coil, which consists in winding the' wire on a specially formed collapsible mandrel having a zigzag contour along one element thereof decreasing in depth peri herally thereabout to a continuous or strai ht line along the diametrically opposite e ement, withdrawing the mandrel from the coil and then bending the coil to cause its ends to approach each other, whereby the segmental conformations of the coil due to the zigzag contour of the mandrel will interlap to accommodate the gradually decreasing pethose of said first wire,

riphery of the torus from the outer to the inner periphery thereof.

12. The method of forming a toroidal coil, which consists in winding a wire into a generally cylindrical 'form in. segmental groups to determine a regular zigzag crosssection along one element of the helix cylinder, gradually decreasing in depth about the cylinder for merging to a straight line cross-section along the element diametrically opposite the maximum zigzag crosssection and curving the cylinder for approach of its ends, whereby the successive segmented groups of convolutions will lap with respect to each other'to form the torus.

13. The method of forming a toroidal coil, which consists me winding a wire into a generally helical-coil, having turns at uniform intervals substantially circular and intervening turns extending within the cylindrical locus of said first set of turns to lap thereinto in curving the helical into a toroidal coil.

14:. The -method of forming a toroidal coil, which consists in winding a'wire ina generally helical conformation of pitch greater than the thickness of the wire, and winding one or more wires successively in lateral contact with the first wire, in turns of progressively greater diameters than will have a stepped segmented conformation for facility in bending their ends toward each other to form the torus.

15. The combination set forth in claim 14, in which the successive wires are connected in series at their ends.

16. The method of producing a toroidal coil, which consists in winding 3, continuous wire into a generally cylindrical helix having successive convolutions substantially in lateral contact'with each other along one element of the cylinder, and curving the helix to form a torus with the contiguous elements of the convolutions determining one of the limiting peripheries of the torus, said convolutions arranged in small substantially identical groups at the elements diametrically opposite said laterally contact ing par s.

17. The method of forming a toroidal coil, which consists in bringing into contiguity substantially uniformly spaced parts of a length of wire, with the intervening substantially uniform lengths each extend ing in a substantially closed curve in a plane coil, which includes winding a wire into a generally helical coil and binding said helical coil at predetermined intervals lengthwise of the wire from which the helical coil is formed, to maintain said bound points against relative displacement both longitudinally and peripherally of the helical coil, while preserving the flexibility to per.

mit curving the helical coil into a torus.

19. The method of forming a toroidal coil, which consists in winding a wire into a generally helical coil, binding the beginnings and'ends of the various convolutions of the coil to prevent relative displacement thereof both longitudinally and circum- -ferentially of the coil, and curving the 'helical coil into a torus with the binding means determining one of the limiting peripheries of the torus.

20. The method of forming a toroidal coil, which includes winding a length of wire into a generally helical coil about a mandrel, binding the beginning and ehd of each convolution, to prevent relative displacement of the wire both longitudinally and peripherally of the coil, while leaving exposed the length of each convolution between its bound' ends, withdrawing the mandrel, and curving the coil thus formed into a toroidal shape;

21. The method of winding a toroidal coil, which includes winding a wire into a plurality of contiguous convolutions about a mandrel and sin'iultaneously binding the beginning and ends of the various convolutions to prevent radial expansion to the convolutions and to insure contiguity of all of the convolutions along a common line when the coil is ren'loved from the mandrel.

22. The method of forming a toroidal coil, which includes winding a length of wire into approximately helical forn' about a mandrel, attaching a binding strip toone side of the helix in such a manner that when the helix is removed from the mandrel, the strip will prevent radial expansion of any of the convolutions thereof and preserve inanil'rel, binding all of the. convolutions of said wire longit-iu'linally ot the mandrel and leaving exposed -the manor portions of the convolutions, withdrawing the mandrel, and

common line of contiguity, removing curving the coil thus formed into a toroidal shape.

24. The method -of forming a toroidal coil, which includes winding av length of wire about a mandrel into a series of contigous convolutions to produce an approximately helical coil, binding the-convolutions while the wire is on the mandrel in such a manner as to prevent change in the diameter thereof, removing the helical coil from the. mandrel and curving it into toroidal form.

25. The method of forming a toroidal coil, which includes winding a length of wire in a series-of contiguous loops about a mandrel, securing a binding strip to the wire on the mandrel in such a manner as to prevent variation in the diameter of the loops or separation of the loops along one the coil from the mandrel, and curving the coil thus fOl'll'ltfl into toroidal shape.

26. The method of forming a toroidal coil, whichconsistsin winding a \vire'into a generally helical coil having turns at uniform intervals of a definite shape and intervening turns extending within the generally cylindrical locus of said first set of turns, and binding the beginnings and ends of all of the convolutions of said coil to prevent relative displacement thereof longitudinally or circumferentially of the coil, and curving the helix into a torus with the binding means atthe outer periphery and the intervening turns-lapping into the first-mentioned turns.

27. The method set forth in claim 2ti, in which separation of the opposite ends of the constituent helical coil is prevented by the step ,of connecting together the opposite ends of the binding.

28. The method of forming a toroidal coil, which includes winding a wire into an approximate.helix including a series of sets of loops, the loops of each set being otf progressively increasing sizes and all of the loops of all of the sets being contiguous to adjacent loops along a straight line at one side of the helix, applying a binder along the common contiguous portions of the loops, curving the coil thus produced into toroidal shape and securing its ends together.

- Signed at-New York city in the county of New York and State oti Ne\v York this 4th day of March A. D. 1924.

FRAN ii A Ul' Y. 

